1. Field of the Invention.
This invention relates to an apparatus for driving a distributor and a fuel pump of a spark ignition internal combustion engine.
2. Description of the Prior Art.
The distributor of a conventional spark ignition internal combustion engine is driven by a driving gear on a cam shaft of the engine, which meshes with a driven gear provided on a rotating distributor shaft. The mechanical fuel pump, which is usually a diaphragm pump, is also driven by the cam shaft, but through an operating lever which engages a drive cam on the cam shaft.
In a typical design, the distributor drive gear and the fuel pump drive cam are axially juxtaposed and are made as a single integral unit of annular shape which is fixed to the cam shaft. Direct high frequency hardening and annealing treatments of the drive cam for reducing its frictional wear invariably give rise to drawbacks such as internal distortion of the cam, which necessitates a further grinding operation to correct the inner bore of the unit, and the creation of scale on the outer peripheral surface of the cam, which has to be removed by barrel grinding. In addition, if the high frequency hardening and annealing process is not uniform over the entire cam surface which engages the pump lever, uneven wear of the lever and the cam could result. On the other hand, should part of the distributor drive gear be affected by the high frequency hardening and annealing, that part of the gear would be hardened and thus shorten the service life of the gear hobbing machine.